1. Field of the Invention
The invention relates to an arrangement for converting a sequence of digital input code words occurring with a first sampling frequency (f.sub.s) and representative of changes in the instantaneous amplitude of a data signal (differential code) into a sequence of output code words occurring with a second, higher sampling frequency (mf.sub.s) and characterizing the instantaneous amplitude of the data signal (absolute code).
The invention stems from the field of the code converters for converting a first code format into a second code format, while simultaneously increasing the sampling frequency.
2. Description of the Prior Art
Such a code converter is disclosed in published Dutch Patent Application 7307237 (PHN 6911). In the embodiment of FIG. 1 of that patent application a sequence of digital input code words which characterize the instantaneous amplitude of a data signal is applied with sampling frequency f.sub.s to a non-recursive interpolating digital filter. At the output of the interpolating filter output code words occur which are also representative of the instantaneous amplitude of the data signal but whose sampling frequency (mf.sub.s) exceeds the sampling frequency (f.sub.s) of the input code words, these output code words then being converted by means of a delta modulation coder into code words characterizing the changes in the instantaneous amplitude of the data signal.
In practice the need was felt for an arrangement for converting DPCM into delta modulation. The code converter as described in the above-mentioned Dutch Patent Application can be used to this end if the differential code (DPCM) is first converted into an absolute code (PCM) by digital integration of the input code words. Such an arrangement has, however, the drawback that a large storage capacity is required in the interpolating filter for storing the integrated input code words.